1. Field of the Invention
The present invention relates to a process for guiding a web, in particular a paper web, such as a continuous paper web or a paper strip cut therefrom, in a web manufacturing or treatment process with the aid of a pneumatically supported device.
2. Discussion of Background Information
Pneumatic support devices for guiding a paper web, or at least a paper strip cut therefrom, are disclosed, for example, in EP 0 232 689 A2. In such pneumatic support devices, one can generally distinguish between compressed air guidance devices that create air cushions with jets and guide media on which the paper sheet or paper strip is guided, and suction and transport devices that create a vacuum with the paper sheet or paper strip and guide the same to a concurrently running perforated endless conveyor belt.
For example, suppose a paper sheet has to be guided at a high rate of speed from the last cylinder of a drying cylinder group of a paper manufacturing process to the roll opening of a calender. For this purpose, a wide strip of paper (e.g., 20-40 cm) is cut off from the running paper sheet behind the last drying cylinder and is guided to the first roll opening of the calendar with known pneumatically supported devices. Meanwhile, the larger portion of the paper sheet, which can have a width of approximately 8 m, is guided back to pulp treatment. Only when the strip successfully passes to the next treatment step in the paper manufacturing process (in the selected example the calender), is the strip gradually cut wider by moving cutting knives across the paper sheet until the entire paper sheet width runs to the next treatment station.
The guidance of the strip is often associated with significant difficulties adjusting the correct air pressure (either too much pressure for the jets, or too little suction pressure on the perforated conveyor belts). In particular, if the paper quality of new products changes--here principally the weight--or the paper sheet speed, the pressures have to be newly adjusted, which is costly, time-consuming, and can lead to significant waste, since one has to wait for the width cut of the paper sheet until the strip has been properly guided to the next treatment station.